This invention relates to wheelchairs with two large wheels and two small wheels and to suspension systems for the small wheels.
Providing a suitable shock absorbing suspension system for the small wheels of wheelchairs has been an ongoing problem. A suitable system will maximize the functionality of the wheel chair through minimal suspension system height to provide better chair stability, minimal forward extension in front of the wheel in order to avoid collision with chairs, tables, curbs and other obstacles, and minimal trailing of the small wheel to avoid loss of stability and avoid contact between the small wheel and the chair and or rider when making turns, while using the largest diameter for the small wheels as is practical.
The suspension system of the present invention was designed to solve problems with prior art suspension systems concerning the height of the suspension system, the trail of the small wheels, the forward extension of the suspension system and the ease of tuning of the suspension system. In addition, the present invention allows the use of small wheels of maximum practical diameter.
U.S. Pat. No. 4,132,423 discloses a strut extending before the small front wheels of wheelchairs having an arcuate rocker end and attached to the wheelchair by a prestressed spring. The strut engages the curb and lifts the small wheelchair wheels, allowing the wheelchair to mount the curb.
U.S. Pat. No. 4,455,031 discloses independent front wheel suspension for a wheelchair. Each front wheel is mounted on an arm which extends from the front wheel across the width of the wheelchair to a location near the other front wheel where the arm is pivotally attached the frame. A coil spring attached to the arm and wheelchair frame near the front wheel provides cushioning.
U.S. Pat. No. 4,572,533 discloses wheelchair front wheels attached to the frame via a tubular shock absorber with coil springs arranged above and below the attachment point of the wheels to the frame.
U.S. Pat. No. 5,464,271 discloses a bicycle seatpost having an upper and a lower piece joined by a pivot pin. A spring biases the two pieces apart. The pieces oscillate with alternate compression and expansion of the spring as the bicycle traverses a bumpy road. The scope of the oscillation is limited by a bolt which connects the pieces and extends through a slot in the arms of the upper piece.
U.S. Pat. No. 5,489,139 discloses a bicycle seatpost with two linkages in the form of a parallelogram and an elastic block which connects two parallel sides of the structure. Compression and expansion of the elastic block results in a smooth ride over rough terrain.
U.S. Pat. No. 5,848,658 discloses a power wheelchair with a stabilizer mechanism for the non-steering front wheels. The mechanism is constructed of an upwardly inclined spring loaded arm connected to the front wheel axle and an approximately horizontal arm also connected to the wheel axle at one end and connected to the frame through a spring loaded shock absorber at the other end.
Invacare Corporation, Elyria, Ohio, produces the INVACARE TOP END TERMINATOR SS everyday chair with FROG LEG suspension castors, which support the front wheels. Each of the front wheels has a polymer shock absorber located directly below the swivel attachment of the wheel to the chair frame.
None of the prior art small wheel suspension systems provide the advantages of the present invention, which includes minimal suspension height, minimal protrusion forward of the vertical connector, and minimal trailing of the wheel during chair movement, combined with the maximum wheel diameter practical.
The invention is a wheel suspension system in which a frame member is suspended by a lower portion to a receptor which swivels about a vertical axis, a wheel axle is spaced from the receptor and pivotally connected to it by a link, the receptor and link having an internal space into which an elastomer block is fitted, and the elastomer block is positioned adjacent to the vertical axis.
In particular, the invention is a small wheel suspension system for wheelchairs having a wheelchair frame. The system comprises a wheel which rolls along the ground and supports the wheelchair. A link having at least one arm is attached to the wheel axle.
The link is attached to a receptor by a pivot pin and the receptor is attached to the wheelchair frame by a vertical connector. The receptor swivels about the vertical connector when the chair changes direction of movement and the wheel so that the wheel axle is behind the vertical connector when the wheelchair is in motion. The link is pivotally connected to the receptor by a horizontal pivot pin, the link pivoting from its position when the wheel encounters an obstacle. An elastomer block positioned between the link and receptor cushions the pivoting of the wheel and link, the elastomer block being compressed when the link pivots. The compressed elastomer block biasing the link toward its original position. The elastomer block is positioned above the wheel axle, before or below the receptor pivot pin, and before the vertical connector when the wheelchair is in motion.
This invention includes a new suspension system for the small wheels of a wheelchair or other similar vehicle. In such a system, a portion of the wheelchair, at the front or rear, is supported by small wheels, which are attached by an axle to a link, generally fork shaped, with one arm on either side of the wheel. Optionally, a link can have only one arm. A receptor is attached to the wheelchair frame and swivels about a vertical connector, which may be a stembolt, thereby allowing the wheel to swivel in order to change the direction of the wheelchair movement. The wheel trails during wheelchair motion, that is, the wheel axle is behind the connector during movement of the chair. The link is attached to the receptor by a pivot pin extending through a hole in the receptor so that the link with attached wheel pivots upward toward the frame and generally toward the rear of the chair when the chair is moving forward and the wheel encounters an obstacle on the ground, such as a rock or unsmooth pavement. Pivoting also occurs to a lesser degree in normal use due to the weight of the user. This pivoting motion of wheel and link is termed xe2x80x9cdeflection.xe2x80x9d In this application, the convention will be followed of designating the rotation of a wheel as clockwise when a wheel on the wheelchair is viewed from the right side of the chair and the chair is moving forward, that is, in the direction the chair occupant is facing. In the first three embodiments, the pivot pin which connects the link and receptor is located in front of the vertical connector when the chair is moving forward. An elastomer block is positioned between the receptor and the link so that the elastomer block is compressed when the link and wheel pivots upward toward the wheelchair frame. The elastomer block also biases the wheel downward toward the ground and toward the front of the wheelchair in a counterclockwise motion. In the first three embodiments, the elastomer block is positioned between the receptor and link above the wheel axle, below the receptor pivot pin and before the vertical connector.
A fourth embodiment suspension system maximizes the diameter of the small wheel while retaining the lower system height and other advantages of the first three embodiments. Small wheels of a relatively greater diameter are especially appropriate for powered wheelchairs. In this fourth embodiment, the pivot pin is located directly under the vertical connector while the elastomer block is located above the wheel axle, in front of the pivot pin and before the vertical connector. The elastomer block may be tilted, as in the first three embodiments. This allows the use of a small wheel of maximum diameter.
Adaptation of the wheelchair characteristics to the requirements of the individual user is termed xe2x80x9ctuning.xe2x80x9d This suspension system is designed to facilitate tuning the system. This system optimizes the amount of trail of the front wheel in order to maintain support under the front of the chair, and to avoid contact between the small wheels and the chair occupant. This system minimizes the height of the suspension system in order to maintain stability of the wheelchair. Finally, this system minimizes the extension forward of the vertical connector in order to reduce contact with obstacles in front of the chair.
One objective of the invention is to provide for easy replacement of the elastomer block to facilitate tuning of the system.
Another objective is to reduce the height of the suspension to maintain stability of the wheelchair.
Another objective is to reduce the trail of the small wheels to maintain the support of the wheelchair and to avoid contact between the wheels and the chair occupant or the chair structure when making a turn.
Another objective is to reduce the forward extension of the suspension system to avoid contact with obstacles before or behind the chair.
Another objective is to facilitate the installation of wheels of various diameters to facilitate tuning of the system.
Another objective is to allow the use of maximum diameter small wheels without interference between the wheels and receptor at maximum wheel deflection.
A final objective of the invention is to provide a small wheel suspension system, which is inexpensive, easy to manufacture, and without adverse effect on the environment.